Injection of animals with naked DNA of mammalian expression vectors induces cellular and humoral immune responses against the encoded protein. We have demonstrated that introduction of naked DNA into the superficial skin induces long lasting humoral and cellular immune responses, which are not obtainable by conventional protein immunization. Furthermore, these immune responses can be modulated specifically by administration of cytokine genes. The Specific Aims of the proposed experiments are: (1) to compare the efficacy of intradermal (i.d.) and intramuscular (i.m.) genetic immunization with different antigen/gene system in triggering cellular and humoral immunity. (2) to modulate immune responses by an "immunological window" approach, i.e., by in vivo transfection of cytokine genes into a localized area of the superficial skin prior to delivery of the given protein antigen to the same site. (3) to elicit immune responses specific for TH1 or TH2 lymphocytes by conditioning the superficial ski with specific TH1 related cytokine genes (IL-2, IL-12, and INFgamma) or TH2 related cytokine genes (IL-4, IL-5, IL-6 and IL-10), respectively. (4) to induce a shift from an already established (committed) antigen specific TH2 response in vivo to a TH1 response, and vice versa, by applying the principals of the immunological window. The proposed studies will establish the basic principles of genetic immunization and of immune regulation by cytokine gene delivery using well defined animal models. The results should enable us to design strategies for genetic manipulation of human immune responses to infectious agents, allergens, autoantigens and tumor associated antigens.